reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?id=1a9e8743248fb63fc15a6168d458e322e320e02b
        git remote add crng-random git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git
        git fetch --no-tags crng-random vdso
        git checkout 1a9e8743248fb63fc15a6168d458e322e320e02b
        make W=1 O=/tmp/kselftest headers
        make W=1 O=/tmp/kselftest -C tools/testing/selftests
        make W=1 O=/tmp/kselftest -C tools/testing/selftests/bpf